AR15, thanks for your commenst and explanations. But there's still something about it that doesn't seem right.

If you're referring to the side adjustment (focus or parallax, whatever one chooses to name it) being set to a range but the target image from that range isn't in sharp focus, then I understand what you're saying.

Nightforce NXS scopes do not have yardage markings on the parallax knob.
You just adjust by eye.
Nightforce is usually pretty good about getting the target image in focus while the reticle is parallax error-free.
This particular scope was an anomaly in my experience.

Schmidt and Bender do have distance markings on the parallax knobs.
Schmidt and bender optics are very good quality and the scopes have a very narrow depth of focus.
It's common to be able to use a Schmidt and bender scope as a rangefinder by sweeping through the focus (parallax adjustment) and finding the near and far limits of where you see sharp focus.
For example, a target placed at 300yds may show sharp image focus from 290 to 310 on the parallax knob.
You can reliably say that target is at 300yds after racking though the focus and splitting the focus range in the middle.
Now, the scope will not always be parallax error free at the 300yd marking through.
You still have to bob your eye around behind the scope and remove the parallax error that way.